Lubricating grease compositions



Patented Dec. 13, 1949 LUBBICATING GREASE COMPOSITIONS Alan Beer-bower,Baltimore, Md, and Arnold J. Moi-way, Clark, N. 1., assignorsto'standardOilDevelopment Company, a corporation of- Delaware No Drawing.Application October 11, 1947,

Serial N 179,408 r I The present invention-relates to lubricating greasecompositions and particularly to greases of improvedviscosity-temperature characteristics having desirable adhesive andnon-spatter properties.

It has been suggested previously that greases of goodviscosity-temperature characteristics may be,prepared by using certainesters as the lubricating medium with lithium soap .as thickeningagents. A prior patent, No. 2,436,347,

issued on a copending application, Serial No..

570,784, filed December 30, 1944, by John C. Zimmer and Arnold J.Morway, shows that a number of esters having the general formulaR1OOC(R)COOR2, where R is a bivalent aliphatic hydrocarbon radical, andR1 and R2 represent alkyl radicals, have excellent lubricatingproperties and excellent temperature characteristics.

As further described in said Zimmer and Morway patent, greases whichhave particularly desirable low-temperature characteristics may beprepared by using the aliphatic dibasic acid esters, such as esters ofaliphatic dicarboxylic acids, for example, esters of malonic, succinic,glutaric, azelaic and sebacic acids, among others.

It is also known that certain polymers, such as polybutene, may impart acertain tackiness or stringiness to mineral oil greases, but suchpolymers are somewhat deficient in stability when subjected to severemechanical working, as in certain types of grease dispensing equipment.In addition, such polymers are otherwise deficient when used with estertype lubricants, as pointed out more fully below.

The present invention relates to specific improvements in the ester typegreases referred to in said copending application and is particularlyconcerned with imparting adhesive or tacky properties to such greases.It has been found that most of the polymers commonly used for impartingstringiness and adhesive properties for lubricants are not suitable foruse in ester type lubricating greases. For example, stringiness agents,such as polyisobutylene, which are widely used in many lubricants, arequite insoluble in esters of the character referred to above.

On the other hand, ordinary methacrylate type polymers which also havebeen used as mineral oil thickeners, for example in hydraulic oils, areunsuitable for use with the dibasic acid esters because they are soextremely soluble in the esters that they do not impart appreciablethickening properties thereto. Hence they do not lend the desiredadhesive or stringiness prop- 11 Claims. (01. 252-42) erties tolubricating compositions of the ester type. It appears to be necessaryto employ as a tackiness agent, a polymer having only a mod erate orborderline degree of solubility in the major components of the grease.One of the objects of this invention is to select a compound having thedesired marginal solubility characteristics and having also adhesive ortacky properties which are not destroyed by the ester, soap or othergrease ingredients.

We have found that ester type greases may be thickened and renderedtacky and adhesive in character by the use of certain polymers ofacrylic acid iso-alkyl derivatives. For example, a suitable material isisobutyl methacrylate polymer of relatively high molecular weight, forexample, in

the range from 50,000 to 400,000 preferably from 100,000 to 300,000. Thesolubility of this polymer in dibasic acid esters, such asdi-Z-ethylhexyl sebacate, is in the desired marginal solubility range toimpart stringiness without the polymer separating from the oil phasebecause of 'too high a degree of insolubility or providing merely aslight thickening action because of too high a degree of solubility.

A typical composition according to the present invention may consist of3 to 25% by weight of lithium soap, such as lithium stearate, 97 to of adibasic acid aliphatic ester, for example, di-Z-ethylhexyl sebacate, and0.1 to about 5% of an iso-alkyl methacrylate polymer, for example,isobutyl methacrylate polymer, said polymer having a molecular weightranging between 50,000 and 400,000, preferably between about 200,000 and300,000.

More specifically, an example of a preferred composition may be given as13% by weight of lithium stearate, 86.5% of di-Z-ethylhexyl sebacate,and 0.5% of isobutyl methacrylate. The resulting grease is a smooth,opaque, stringy material which shows less tendency to separate the oilyester than the corresponding lithium stearate-ester grease made withoutthe polymer. The grease shows good resistance to spattering whensubjected to sudden shock loading which is requisite for operation atelevated temperatures.

A grease having the composition just described may be prepared asdescribed in the aforesaid patent. Preferably the soap is made first byreacting a suitable fatty material such as tallow, stearic acid,hydrogenated fish oil acids, or the like, with the appropriatesaponification agent, preferably an alkali metal hydroxide, e. g.sodium, potassium, or lithium. The soap thus formed representative ofthe radicals R1 and R2.

- 3 may be dried, and may be-powdered, if desired, to facilitate itssolution in the liquidester. On the other hand, in the case of certainmetal hydroxides or oxides used to saponifythe fatty material, suchaslithium,- calcium, magnesium, or aluminum hydroxides, the soap may beprepared by the well known process of precipitation from water.

The required amount of soap is then added to the ester and the mixtureis heated to a temperature of about 300 to 450 E, preferably 350' to 400F., until the soap is completely melted in the ester. Thereafter thepolymer and other modiilers are added, preferably during cooling whilemechanical mixing is continued. Generally it is preferred to add themodifiers after the temperature has dropped materially, e. g. after thetemperature has been brought down to about 250 or 200 F.

It will be understood that the quantities of lithium or other metal soapand of the methacrylate polymer may be varied somewhat depending uponthe final characteristics desired. Thus the soap content may be variedfrom 3 to 25% by weight based on the total composition and themethacrylate polymer may be used in quantities as little at 0.1% to asmuch as 5% or more, on the same basis.

In lieu of di-2-ethylhexyl sebacate, most of the various other dibasicacid esters enumerated above and more fully described in said copendingapplication may be employed. Esters such as isobutyl sebacate, and ingeneral, the esters of dibasic acids having 3 to 12 carbon atoms, suchas malonic, succinic, isosuccinic, glutaric, ethyl malonic,pyrotartaric, adipic, pimelic, suberic, azelalc, and sebacic acid aresuitable. Instead of one of the acids enumerated above, any acid ormixture of acids having the general formula HOOC(R)COOH may be usedwhere R is a bivalent aliphatic hydrocarbon radical. Any of these estersmay be used also in combination with moderate quantities of mineral baselubricating oil of appropriate viscosity. Various synthetic aliphaticacids produced by the polymerization or dimerization of unsaturatedfatty acids or their esters may be used as will be understood by thoseskilled in the art. The acids themselves are preferably saturated butthe unsaturated acids also maybe used.

As indicated briefly above, the esters employed have the generalformula.

where R is a bivalent aliphatic hydrocarbon radical such as methylene,polymethylene, ethylidene, propylidene, methyl dimethylene,butenylidene, and the like, and R1 and R2 are similar or dissimilarhydrocarbon radicals, such as branched chain alkyl, and cycloalkyl,radicals. Secondary butyl, cyclohexyl, and secondary octyl phenyl areEsters containing aromatic nuclei are not considered satisfactorybecause of their poor viscosity index. The esters may contain additionalsubstituents or functional groups such as Cl, Br. NHaNHR, NR1R2, CHO,CO, SH, SR, RSSR, ROR, and RO-Metal. They may be prepared by any of themethods known to the prior art. One particular method of preparing theester is to react the alcohol with the acid at elevated temperatures inthe presence of a suitable esterification catalyst such as sulfuricacid, sulfosalicylic acid, etc., as

4 set forth more fully in the aforesaid copending application.

It will be understood that lubricating compositions of this inventionmay contain varying proportions of esters with other ingredients such asmineral oil or other esters. It will also be understood that variousoxidation inhibitors, such as phenolic or amine types, for example,phenyl alpha naphthylamine, may be employed in suitable proportions.Other suitable oxidation inhibitors are, phenyl beta naphthylamine,aldol alpha naphthylamine, ditertiary butyl para cresol, and the like,with or without synergistic agents, such as ammonia-formaldehydedi-isobutyl condensation product. Other or additional ingredients, suchas oiliness agents, rust inhibitors, extreme pressure additives, and thelike, may be incl tided as will be apparent to those skilled in the aWhile lithium stearate has been specifically mentioned as the preferredcomposition for thickening the ester-type lubricant to a grease, it willbe understood that various other materials may be substituted. Thusother soaps of lithium, such as those derived from hydrogenated fish oilacids, may be employed. Soaps of other metals such as barium, calciumand sodium may be employed. In general, lithium soaps of preferablysaturated or substantially saturated fatty acids having 12 to 24 carbonatoms per molecule are preferred but the soaps of correspondingunsaturated acids, or of mixtures of such saturated and unsaturated, maybe used.

In lieu of soaps, other thickening agents which are suitable forimparting grease-like structure to the lubricant may be employed. Amongthese are carbon black, especially acetylene black which has pronouncedstructural characteristics, silica gel, and silica of the type which isprepared by condensing the smoke from heated ethyl silicate.

It will be understood further that although the particular polymer,isobutyl methacrylate, is preferred for use with the dibasic esters ofbranched chain alcohols, such as the isopropyl, secondary butyl and2-ethylhexyl derivatives, other iso-alkyl methacrylate polymers may beused, provided their solubility characteristics and tackiness andstringiness properties in the particular lubricant are comparable withthose of isobutyl methacrylate polymer in, say di-2-ethylhexyl sebacate.The

polymer should be just moderately soluble in the ester orester-containing liquid lubricant, as noted above. Other polymers of asimilar nature may be used, such as isopropyl, normal butyl, and variousamyl methacrylates, provided their solu; bility range is suitable.

The liquid lubricant which forms the basis of the improved greasesincluded in the present invention may be composed entirely of a singledibasic acid ester of branched chain alcohol, or it may consist of amixture of several such esters. Further, it is found that esters of thischaracter may be mixed in various proportions with mineral baselubricating oil of appropriate grade and viscosity. In general, theester content of the liquid should be 75% or at least 50% by weight ofthe finished grease composition. The remainder may be mineral oil oranother ester, or mixtures thereof, thickened by a suitable soap, carbonblack, silica gel, or other inorganic thickeners.

Regarding the esters of the type 'COOR1(R) COORz, where R is analiphatic bivalent hydrocarbon, the

branched chain radicals R1 and R: preferably are those having not lessthan three and not more than about 12 carbon atoms each. R1 and R: maybe alike or dissimilar. The dibasic acid radical preferably has not lessthan 3 nor more than 12 carbon atoms, those having from 3 to carbonatoms being preferred. These aliphatic compounds are preferablysaturated, although unsaturated compounds may be used. They are not as 1readily available, as a rule, as the saturated compounds. As notedabove, the aromatic compounds are not favored because of their usuallylow viscosity index.

We claim:

1. A tacky lubricating grease composition consisting essentially of 70to 97% of a dibasic acid ester having the general formula coon,

where R is a bivalent aliphatic hydrocarbon radical and R1 and R: arebranched chain hydrocarbon radicals, 3 to 25% of a lithium-soap ofessentially saturated fatty acids having 12 to 24 carbon atoms permolecule, and 0.1 to 5% of an C: to C5 alkyl methacrylate polymer ofmolecular weight between 50,000 and 400,000, said polymer having amoderate but limited solubility in said ester so as to impartsubstantial tackiness and stringiness properties to said composition.

2. A lubricating grease composition consisting essentially ofdi-Z-ethylhexyl sebacate containing 3 to 25% by weight, based on thetotal composition, of a lithium soap of a fatty acid having from 10 to24 carbon atoms per molecule and 0.1 to 5% of isobutyl methacrylatepolymer of molecular weight between 50,000 and 400,000 as a stringinessagent. F

3. A lubricating grease composition consisting essentially of 70. to 97%by weight of dibasic acid ester of branched chain aliphatic alcoholswherein said acid radical contains 3 to 12 carbon atoms and said alcoholradicals contain 3 to 12 carbon atoms each, 3 to 25% of av grease typethickener, and 0.1 to 5% of polymerized isobutyl methacrylate having amolecular weight between 50,000 and 400,000.

4. A lubricating composition consisting essentially of a liquidlubricant composed of at least 50% by weight of an aliphatic dibasicacid ester of branched chain alcohols, 3 to 25% by weight of I athickening agent to imparta grease-like structure to said composition,and 0.1 to 5% of an C: to Cs alkyl methacrylate polymer having amolecular weight range between 50,000 and 400,000

acid having 12 to 24 carbon atoms per molecule, and 0.1 to 5% ofisobutyl methacrylate polymer of molecular weight range between 100,000and 300.000. 7 7. A lubricating composition consisting essentially ofdi-2-ethy1hexyl sebacate containing 3 to 25% by weight, based on thetotal composition, of lithium stearate and 0.1 to 5% ofan isobutylmethacrylate polymer of a molecular weight range between 50,000 and400,000.

8. A lubricating grease composition consisting essentially of 13%lithium stearate, 86.5% di-2- ethylhexyl sebacate and 0.5% of anisobutyl methacrylate polymer having a molecular weight range between50,000 and 400,000 and having border line solubility characteristics insaid other ingredients to impart stringiness to said grease composition.

9. A lubricating grease composition having adhesive propertiesconsisting essentially of an oily lubricant containing to by weight ofan aliphatic dibasic acid ester of branched chain alcohols and 50% to 0%of mineral oil, 3 to 25% by weight, based on the total composition, of athickening agent to impart colloidal grease-like properties to saidlubricant, and 0.1 to 5% of a marginally soluble C3 to C5 alkylmethacrylate polymer having a molecular weight range between 50,000 and400,000.

10. Composition as in claim 0 wherein said polymer has a molecularweight range of 100,000 to 300,000.

11. Composition as in claim 9 wherein said polymer is isobutylmethacrylate. v

ALAN BEERBOWER. ARNOLD J. MORWAY.

REFERENCES CITED The following references are of record in th ille ofthis patent:

UNITED STATES amma Number Name Date 2,104,408 Wiezevich Jan. 4, 19382,274,673 Earle Mar. 3, 1942 2,409,333 Wright et al. Oct. 15, 19462,436,347 Zimmer et al Feb. 17, 1948 2,448,567 Zisman et a1. Sept. 7,.1948

OTHER REFERENCES Balm et al., Synthetic Low Temperature Greases fromAliphatic Diesters, article in Industrial and Engineering Chemistry,vol. 89, DD. 500-508, April 1947. I

